Not entirely smart trip (5)
I believe the answer is:
sport
'trip' is the definition.
(thesaurus)
'not entirely smart' is the wordplay.
'not entirely' means to remove the last letter (not all of the word).
'smart' becomes 'sporty' (I've seen this in another clue).
'sporty' with its last letter removed is 'SPORT'.
(Other definitions for sport that I've seen before include "eg Tennis" , "Wear, display (an item)" , "Recreation, play" , "Exhibit publicly; eg soccer" , "Physical recreation" .)